The invention relates generally to disc brakes, such as the type commonly used on automotive vehicles. More specifically, the invention relates to such disc brakes configured to reduce the amount of brake noise encountered during low-speed brake applications.
Conventional hydraulically-actuated disc brakes include a hydraulic piston slidably movable within a piston bore formed in the disc brake caliper. Hydraulic pressure generated upon application of the brakes by an operator urges the piston inwardly toward the brake rotor (which rotates about an axis), which in turn (due to the reactive force of the caliper) causes the brake pads on opposite sides of the brake rotor to exert compressive braking forces on the rotor, slowing or ultimately halting its rotation. During this operation, the backing plates on the brake pads cause braking torque loads to be reacted against one or more rails or pins that are oriented in an axial direction normal or perpendicular to the brake pad backing plates and thus the brake rotor.
Due to the thickness of the pad backing plates and the brake pads themselves, braking forces generated at the pad-to-disc interface are offset (in an axial direction) from the outboard surface of the backing plate, thus producing force couples that cause the leading edges of the pads to compress against the rotor to a greater extent than the trailing edges of the brake pads. This tends to cause an unstable "biting in", "chattering" or "scuffing" effect on the rotor, resulting in increased brake noise, usually in the form of high frequency squeal, especially when the brakes are applied at low speeds.
With a view toward substantially minimizing this instability and significantly reducing low-speed braking noise, the present invention provides a hydraulic piston and piston bore (or other brake actuating element), that is angled away from the normal direction perpendicular to the pad backing plate and to the rotor. Thus the brake-applying forces are directed in an inward angled direction, generally toward the rotor and toward the leading edge of the brake pads. Preferably, this angulation between the centerline of the piston bore (or the force centerline of other types of actuators) and the above-mentioned normal direction is defined by rotating the piston bore centerline circumferentially about an axis defined by a line lying at the piston-to-backing plate interface, parallel to the plane of the rotor disc-to-pad rub track and passing through the rotor's axis of rotation, although other angle apex locations (closer to or farther from the rotor) may also be used. Such an arrangement results in reactive forces (due to the above-mentioned angled brake-applying forces) on the brake pads that cause them to exert a greater (or at least equal) compressive force on the rotor at the trailing edge of the brake pads when compared to the leading edge of the brake pads (when the vehicle is traveling in a forward direction). The magnitude of this effect depends in part on the amount of caliper free play in the axial and/or circumferential directions. This reversal of the leading and trailing magnitude relationship of the compressive forces (as compared with conventional brake designs) significantly increases the stability of the brake components when the brakes are applied and results in significantly minimized braking noise, especially at low vehicle speeds when such brake noise is typically most significant. Additionally, if found to be advantageous (for example, to reduce pad taper wear) in a particular brake configuration or pad geometry, the piston bore centerline (or other actuator centerline) can be angled in a radial direction (toward or away from the rotor's axis) in lieu of, or even in addition to, the above-mentioned circumferentially angled direction.
Additional objects, advantages, and features of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings.